Several types of measurement are reported. R.m.s. pressures in one-eighth-second intervals, from the speech of a single voice, are compared with similar measurements in one-fourth-second intervals. The values obtained in the first case are only slightly more widely distributed than in the second, and the difference is least when attention is confined to high frequencies. To earlier r.m.s. measurements, on the voices of six men and five women, is applied the relation found more recently between pressure at a point and total voice power. The resulting curves represent average spectra of voice power for the men and women. Measurements of the distribution of instantaneous pressures in speech are also given.

The minimum audible field (M.A.F.) has been determined from data taken on 14 ears over the frequency range from 100 to 15,000 c.p.s. The observer is placed in a sound field which is substantially that of a plane progressive wave, facing the source and listening monaurally. The M.A.F. is expressed as the intensity of the free field, measured prior to the insertion of the observer. Similar data are presented for binaural hearing, over the range from 60 to 15,000 c.p s., obtained with 13 observers. At 1000 c.p.s. the average M.A.F. observed is 1.9 × 10−16 watts per cm2, corresponding to a pressure 71 db below 1 bar. Included are data showing how the M.A.F. varies with the observer's azimuth relative to the wave front. Another type of threshold data refers to minimum audible pressures (M.A.P.) as measured at the observer's ear drum. The differences obviously to be expected between M.A.F. and M.A.P. values are due to wave motion in the ear canal and to diffraction caused by the head. The M.A.F. data are discussed in relation to the M.A.P. determinations from several sources. Some possible causes of difference between the two, which are due to experimental procedure and may add to the causes already mentioned, are pointed out.

Measurements made on instruments and orchestras, during the playing of selections, include average amplitudes in long intervals (15 seconds) and distribution of peaks in very short intervals (one-eighth second). Octave and half-octave bands are measured, as well as unfiltered music. The instruments tested were selected as possibly contributing extreme frequencies and amplitudes. Calculations of peak acoustic powers range as high as 27 watts.Although different techniques would be applied today, such as the use of a recorded tape to insure exact duplication of a selection as different frequency bands are explored, and the measurement of rms rather than average amplitudes, it is nevertheless felt that the measurements were reasonably accurate . The type of presentation, however, left something to be desired. Both kinds of curves will be found here in new forms. For the peaks, the plan used later in presenting similar data on speech1 has been adopted. The average amplitudes are reduced to a per-cycle basis in a different manner. Both types are plotted in absolute rather than relative units, and are reduced to a common distance. The table of peak powers is recalculated, using the same assumptions as before, but making the estimate for the 1 per cent level of intervals, in all cases. All new reductions and calculations are made from the original measured data.

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